In the oil refining industry, the term xe2x80x9calkylationxe2x80x9d is used to describe processes in which isoparaffins (e.g., isobutane) are reacted with olefin (e.g., 1-butene) to form the xe2x80x9calkylatexe2x80x9d or higher molecular weight branched paraffins (typically isooctane or 2,2,4-trimethylpentane in the isobutane/1-butene case). The higher molecular weight branched paraffins produced have desirable high research octane numbers, making the product an excellent blending component for gasoline. Typically, in the example reaction described, a large excess of the 1-butene is used to drive olefin conversion, and the excess isobutane is recovered and recycled.
An important alkylation method is an acid-catalyzed process. Concentrated sulfuric acid and more recently, hydrofluoric acid have been used as the catalyst. However, there has been continuing interest in the development of a solid cata lyst to replace sulfuric and hydrofluoric acids.
A solid-supported liquid catalyst in a moving catalyst zone, through which the alkane/alkene stream can pass, has been reduced to practice by, for instance, Hommeltoft and Topsoe in U.S. Pat. No. 5,245,100, who describe a catalyst of trifluoromethanesulfonic acid (triflic acid CF3SO3H)adsorbed on, inter alia, silica. As the loading is reduced with the Hommeltoft and Topsoe catalyst system, the useful lifetime of the catalyst system decreases sharply to impracticably short time periods.
Clerici, et al., in U.S. Pat. No. 5,659,105, describe an alkylation catalyst composed of a silica-based material having surface Sixe2x80x94OH groups esterified with a linear perfluorosulfonic acid of the formula CF3(CF2)nSO3H, where n is 0-11. Clerici, et al., asserted the catalyst showed higher activity than the triflic acid adsorbed on silica described by Hommeltoft and Topsoe. However, the esterified xe2x80x94Sixe2x80x94OH groups are not stable and are removed from the silica in use.
A further problem is the tendency for the acid catalysts to become deactivated or passified, a process believed to be associated with the formation of stable esters between the strong acid and the feedstock olefin. While such passivation occurs with stationary acid catalysts, the effect is minimized by the flow-through, recovery, and recycle associated with mobile catalysts. Hommeltoft, et al., in Ind. Eng. Chem. Res. 1997, 36, 3491-3497, provide a discussion of such passivation mechanisms. Hommeltoft, et al., report that while the addition of a mobile Lewis acid such as boron trifluoride, antimony pentafluoride, or aluminum chloride does improve the lifetime of the stationary catalyst, it also introduces handling problems with the volatile and hazardous Lewis acid. It is desirable to minimize the mobile acid throughput and recycle.
The catalyst of the present invention provides economies over the sulfuric acid process and a marked reduction in process hazards over the hydrofluoric acid process. Additionally, the catalyst of this invention provides a longer catalyst life over both the acid modified silica and the mobile acid supports of the prior art. By comparison with the mobile acid treated supports of the prior art, the amount of mobile acid required is substantially reduced.
The present invention comprises a catalyst comprising A) a stationary acid component selected from the group consisting of a perfluorinated ion exchange polymer on an inert support, a silane modified perfluorosulfonic acid, and a sulfated metal oxide; and B) a mobile acid component selected from the group consisting of chlorosulfonic acid, fluorosulfonic acid, a fluorinated monosulfonic acid of Formula 1a, a fluorinated sulfonimide of Formula 1b or 1c, a fluorinated disulfonic acid of Formula 2, and an adjunct acid mixture; wherein
Formula 1a is R1xe2x80x94CF2xe2x80x94SO3H,
Formula 1b is (R1xe2x80x94CF2xe2x80x94SO2)2NH,
Formula 1c is R1xe2x80x94CF2xe2x80x94SO2xe2x80x94NHxe2x80x94R2,
wherein each R1 is independently Cl; F; H; branched or straight chain C1 to C10 alkyl optionally interrupted by oxygen atoms and optionally substituted with Cl or F; C6 to C12 aryl; or C6 to C12 aryl substituted with up to two groups selected from the group consisting of Cl, F, C1 to C10 alkyl, and C1 to C10 alkoxy;
each R2 is independently branched or straight chain C1 to C10 alkyl optionally interrupted by oxygen atoms and optionally substituted with Cl or F; C6 to C12 aryl; or C6 to C12 aryl substituted with up to two groups selected from the group consisting of Cl, F, C1 to C10 alkyl, and C1 to C10 alkoxy; and
Formula 2 is HSO3xe2x80x94CF2xe2x80x94R3xe2x80x94CF2xe2x80x94SO3H wherein R3 is a divalent C1 to C10 alkylene optionally interrupted by oxygen atoms and optionally substituted with Cl or F; a C6 to C12 arylene; or C6 to C12 arylene substituted with up to two groups selected from the group consisting of Cl, F, C1 to C10 alkyl, and C1 to C10 alkoxy.
The present invention further comprises an improved alkylation process wherein the improvement comprises reacting an olefin with an alkane in the presence of a catalyst as described above.
The present invention further comprises an improved process for isomerization of at least one alkene wherein the improvement comprises conducting the isomerization in the presence of a catalyst as described above.
The present invention further comprises an improved process for oligomerization of an olefin wherein the improvement comprises conducting the oligomerization in the presence of a catalyst as described above.
The present invention is directed toward an improved catalyst that comprises a new combination of a fixed solid strong acid (hereinafter the xe2x80x9cstationary acidxe2x80x9d, xe2x80x9cstationary acid componentxe2x80x9d, xe2x80x9cheterogeneous acidxe2x80x9d or xe2x80x9cheterogeneous acid componentxe2x80x9d) and a mobile strong acid (hereinafter the xe2x80x9cmobile acidxe2x80x9d, xe2x80x9cmobile acid componentxe2x80x9d, xe2x80x9chomogeneous acidxe2x80x9d or xe2x80x9chomogeneous acid componentxe2x80x9d), and the use of the catalyst in alkylation, oligomerization, and isomerization processes. The catalyst of this invention substantially reduces the concentration of homogeneous acid required in the heterogeneous acid component, thus minimizing the amount of eluted homogeneous acid requiring recovery and recycle.
Specifically, the stationary acid component of this invention comprises (a) a highly fluorinated polymeric sulfonic acid fixed on or entrapped within a porous silica or metal oxide support, (b) a silane-modified perfluorosulfonic acid on silica or metal salts, or (c) a sulfated metal oxide.
In the first embodiment, the stationary acid is a perfluorinated ion-exchange polymer containing pendant sulfonic acid groups dispersed and entrapped within a silica or metal oxide support. Examples of such stationary acid components are a solid acid component such as the NAFION perfluorinated ion-exchange polymer in a silica nanocomposite, as described by Harmer and Sun in U.S. Pat. No. 5,824,622, or a perfluorosulfonic acid grafted on silica as described by Harmer et al. in U.S. Pat. No. 5,958,822 in which the graft is
HO3Sxe2x80x94(CF2)2xe2x80x94Oxe2x80x94(CF2)2xe2x80x94(CH2)3xe2x80x94Sixe2x80x94[xe2x80x94Oxe2x80x94]3xe2x80x94{silica}.
Perfluorinated ion-exchange polymers (PFIEP) containing pendant sulfonic acid, carboxylic acid, or sulfonic acid and carboxylic acid groups used in the present invention are well known compounds. See, for example, Waller et al., Chemtech, July 1987, pp. 438-441, and references therein, and U.S. Pat. Nos. 5,094,995 and 5,824,622. Perfluorinated ion-exchange polymers (PFIEP) containing pendant carboxylic acid groups also have been described in U.S. Pat. No. 3,506,635. Polymers discussed by J. D. Weaver et al., in Catalysis Today, 14 (1992) 195-210, are also useful in the present invention. Polymers that are suitable for use in the present invention have structures that include a substantially fluorinated carbon chain that may have attached to it side chains that are substantially fluorinated. In addition, these polymers contain sulfonic acid groups or derivatives of sulfonic acid groups, carboxylic acid groups or derivatives of carboxylic acid groups and/or mixtures of these groups. For example, copolymers of a first fluorinated vinyl monomer and a second fluorinated vinyl monomer having a pendant cation exchange group or a pendant cation exchange group precursor can be used, e.g., sulfonyl fluoride groups (xe2x80x94SO2F) which can be subsequently hydrolyzed to sulfonic acid groups. Possible first monomers include tetrafluorbethylene (TFE), hexafluoropropylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), and mixtures thereof. Possible second monomers include a variety of fluorinated vinyl ethers with pendant cation exchange groups or precursor groups. Preferably, the polymer contains a sufficient number of acid groups to give an equivalent weight of from about 500 to 20,000, and most preferably from 800 to 2,000. Representative of the perfluorinated polymers for use in the present invention are NAFION PFIEP (a family of polymers for use in the manufacture of industrial chemicals, commercially available from E. I. du Pont de Nemours and Company), and polymers, or derivatives of polymers, disclosed in U.S. Pat. Nos. 3,282,875; 4,329,435; 4,330,654; 4,358,545; 4,417,969; 4,610,762; 4,433,082; and 5,094,995. More preferably the polymer comprises a perfluorocarbon backbone and a pendant group represented by the formula xe2x80x94OCF2CF(CF3)OCF2CF2SO3X, wherein X is H in the practice of this invention. Polymers and alkali metal or ammonium salts of polymers of this type are disclosed in U.S. Pat. No. 3,282,875.
Typically, such perfluorinated polymers are derived from sulfonyl group-containing polymers having a fluorinated hydrocarbon backbone chain to which are attached the functional groups or pendant side chains which in turn carry the functional groups. Fluorocarbosulfonic acid catalyst polymers useful in the practice of this invention have been made by Dow Chemical and are further described in Catalysis Today, 14 (1992) 195-210. Other perfluorinated polymer sulfonic acid catalysts are described in Synthesis, G. I. Olah, P. S. Iyer, G. K. Surya Prakash, 513-531 (1986).
There are also several additional forms of the above polymer catalysts in which the sulfonic acid group is present as a metal salt in the microcomposite of the present invention. These comprise 1) a partially cation-exchanged polymer, 2) a completely cation-exchanged polymer, and 3) a cation-exchanged polymer where the metal cation is coordinated to another ligand (see U.S. Pat. No. 4,414,409, and F. J. Waller in British Polymer Journal, Volume 16, pp. 239-242; and ACS Symposium Series 308; American Chemical Society, Washington, DC, 1986, Chapter 3). The metal cations useful in these additional forms of the above polymer catalysts are Cr3+, Sn2+, Al3+, Fe3+, Co2+, Zn2+, Hg2+, and lanthanides such as Y.
Preferred PFIEP suitable for use in the present invention comprise those containing sulfonic acid groups. Most preferred is a sulfonated NAFION PFIEP.
Typically, such PFIEP materials do not have satisfactory physical properties for them to be used in a fixed bed catalyst column. A more suitable fixed bed form is obtained when the PFIEP is entrapped and highly dispersed within a silica or metal oxide network, wherein the weight percentage of perfluorinated ion-exchange polymer in the microcomposite is from about 0.1 to 90 percent, preferably from about 5 to about 80 percent, most preferably from about 5 to about 20 percent and wherein the size of the pores in the microcomposite is about 0.5 nm to about 75 nm. The terms xe2x80x9corganic-inorganic polymer microcompositexe2x80x9d or xe2x80x9cmicrocompositexe2x80x9d are used to describe this structure.
The organic-inorganic polymer microcomposites of the present invention are high surface area, porous microcompositions that exhibit excellent catalytic activity. Whereas the surface area of NAFION nm 50 PFIEP, a commercial product, is approximately 0.02 m2 per gram, a preferred embodiment of the present invention comprises microcomposites of PFIEP and silica having a surface area typically of 5 to 500 m2 per gram. The composition of the present invention exists as a particulate solid that is porous and glass-like in nature, typically 0.1-4 mm in size and structurally hard, similar to dried silica gels. The perfluorinated ion exchange polymer (PFIEP) is highly dispersed within and throughout the silica network of the microcomposite of the present invention, and the microstructure is very porous. The porous nature of this material is evident from the high surface areas measured for these glass-like pieces, having typical pore diameters in the range of 1-25 nm. Another preferred embodiment is the use of the present invention in pulverized form.
Within the composite, silica is preferred but a metal oxide can be substituted in place of the silica. The term xe2x80x9cmetal oxidexe2x80x9d signifies metallic or semimetallic oxide compounds, including, for example, alumina, silica, titania, germania, zirconia, alumino-silicates, zirconyl-silicates, chromic oxides, germanium oxides, copper oxides, molybdenum oxides, tantalum oxides, zinc oxides, yttrium oxides, vanadium oxides, and iron oxides. The term xe2x80x9cmetal oxide precursorxe2x80x9d refers to the form of the metal oxide that is originally added in the sol-gel process to finally yield a metal oxide in the final microcomposite. In the case of silica, for example, it is well known that a range of silicon alkoxides can be hydrolyzed and condensed to form a silica network. Such precursors as tetramethoxysilane (tetramethyl orthosilicate), tetraethoxysilane (tetraethyl orthosilicate), tetrapropoxysilane, tetrabutoxysilane, and any compounds under the class of metal alkoxides which in the case of silicon is represented by Si(OR)4, where R includes methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl or where R is a range of organic groups, such as alkyl. Also included, as a precursor form is silicon tetrachloride. Further precursor forms comprise organically modified silica, for example, CH3Si(OCH3)3, PhSi(OCH3)3, and (CH3)2Si(OCH3)2. Other network formers include metal silicates, for example, potassium silicate, sodium silicate, lithium silicate. K, Na or Li ions can be removed using a DOWEX cation exchange resin (sold by Dow Chemical, Midland, Mich., which generates polysilicic acid that gels at slightly acid to basic pH. The use of LUDOX colloidal silica (E. I. du Pont de Nemours and Company, Wilmington, Del.) and fumed silica (CAB-O-SIL sold by Cabot Corporation of Boston, Mass.), which can be gelled by altering pH and adjusting the concentration in solution, will also yield a metal oxide network in the microcomposite of the invention. For example, typical precursor forms of silica are Si(OCH3)4, Si(OC2H5)4 and Na2SiO3; and a typical precursor form of alumina is aluminum tri-sec-butoxide Al(OC4H9)3.
In a second embodiment of the present invention, the stationary acid component of the catalyst is a silane-modified perfluorosulfonic acid as described by Harmer et al. in Chemical Communications, 1997, 1803-1804. Specifically, the stationary acid is a perfluorosulfonate/trisilanol having the structure M30 xe2x88x92O3Sxe2x80x94(CF2)2xe2x80x94Oxe2x80x94(CF2)2xe2x80x94(CH2)3xe2x80x94Sixe2x80x94[xe2x80x94Oxe2x80x94]3xe2x80x94{silica}. The hydrolyzed alkoxysilane groups are attached to a silica support as described in the preceding reference and in Example 2 below.
In a third embodiment of the present invention, the stationary acid component of the catalyst is sulfated zirconia. Sulfated zirconia is described by Corma and Garcia in Organic Reactions Catalyzed over Solid Acids, in Catalysis Today, 38, 257-308, 1997, in which see Section 5, Sulfated Zirconia as a Solid Acid Catalyst, pp. 294-300. Other sulfated metal oxides useful in the practice of the third embodiment are sulfated TiO2, Fe2O3, Al2O3, SiO2, and Bi2O3.
The mobile acid component of the present invention comprises (a) chlorosulfonic acid, fluorosulfonic acid, or a fluorinated sulfonic acid or sulfonimide; (b) a fluorinated disulfonic acid; or (c) an adjunct acid mixture.
The first embodiment of the mobile acid component of the catalyst of this invention is selected from chlorosulfonic acid, fluorosulfonic acid, a fluorinated sulfonic acid of the structure of Formula 1a, or a fluorinated sulfonimide of the structure of Formula 1b or 1c:
wherein
each R1 is independently Cl; F; H; branched or straight chain C1 to C10 alkyl or substituted C1 to C10 alkyl fully or partially substituted independently with chlorine and fluorine, the carbon chain of which is optionally interrupted by oxygen atoms; a C6 to C12 aryl; or C6 to C12 aryl substituted by up to two groups selected from Cl, F, C1 to C10 alkyl, and C1 to C10 alkoxyl.
each R2 is independently branched or straight chain C1 to C10 alkyl or substituted C1 to C10 alkyl fully or partially substituted independently with chlorine and fluorine, the carbon chain of which is optionally interrupted by oxygen atoms; a C6 to C12 aryl; or C6 to C12 aryl substituted by up to two groups selected from Cl, F, C1 to C10 alkyl, and C1 to C10 alkoxyl.
A preferred mobile acid of the structure of Formula 1a is triflic acid, CF3SO3H, bp 161xc2x0 C. Most preferred is 1,1,2,2-tetrafluoroethanesulfonic acid, Hxe2x80x94CF2,xe2x80x94CF2xe2x80x94SO3H, bp 245xc2x0 C.
Higher molecular weight mobile acids have progressively diminished volatility and thus facilitate removal of the mobile acid from the product. However, in practice this is offset by the increase in equivalent weight and the need to have a higher weight loading of mobile acid on the support as the equivalent weight increases.
Other examples of Formula 1a useful in the present invention include the linear perfluoroalkane sulfonic acids CF3(CF2)nSO3H wherein n is 1-12 and incompletely perfluorinated sulfonic acids such as 2-chloro-1,1,2-trifluoroethanesulfonic acid, CHClFxe2x80x94CF2xe2x80x94SO3H.
Examples of fluoroether sulfonic acids of Formula 1a useful herein are:
CF3xe2x80x94CF2xe2x80x94Oxe2x80x94CF2xe2x80x94CF2xe2x80x94SO3H,
CH3xe2x80x94CH2xe2x80x94Oxe2x80x94CF2xe2x80x94CF2xe2x80x94SO3H,
CF2Clxe2x80x94CFClxe2x80x94Oxe2x80x94CF2xe2x80x94CF2xe2x80x94Oxe2x80x94CF2xe2x80x94CF2xe2x80x94SO3H,
CF2Clxe2x80x94CFClxe2x80x94Oxe2x80x94CF2xe2x80x94CF2xe2x80x94SO3H,
HClFCxe2x80x94CF2xe2x80x94SO3H, and
HFC(CF3)xe2x80x94CF2xe2x80x94SO3H.
Examples of the sulfonimides of Formula 1b useful herein are (CF3xe2x80x94SO2)2xe2x95x90NH, CF3SO2NHSO2C3F8, and (C4F9SO2)2NH and others as described by Ilmar et al. in xe2x80x9cThe Gas Phase Acidities of Very Strong Neutral Bronsted Acids,xe2x80x9d J. Am. Chem. Soc. 1994, 116, 3047-3057. Examples of the sulfonimides of Formula 1c useful herein are CF3xe2x80x94SO2xe2x80x94NHxe2x80x94SO2xe2x80x94CH3 and CF3xe2x80x94SO2xe2x80x94NHxe2x80x94SO2C6H5.
A second embodiment of the mobile acid component of the catalyst of this invention is a perfluorinated or highly fluorinated disulfonic acid of the structure of Formula 2:
HSO3xe2x80x94CF2xe2x80x94R3xe2x80x94CF2xe2x80x94SO3Hxe2x80x83xe2x80x83Formula 2
wherein
R3 is a divalent C1 to C10 alkylene or substituted C1 to C10 alkylene fully or partially substituted independently with chlorine and fluorine, the carbon chain of which is optionally interrupted by oxygen atoms; a C6 to C12 arylene; or C6 to C12 arylene substituted by up to two groups selected from Cl, F, C1 to C10 alkyl, and C1 to C10 alkoxyl.
Examples of the disulfonic acids of Formula 2 are HSO3xe2x80x94(CF2)nxe2x80x94SO3H where n is 3-12, and HO3Sxe2x80x94CF2xe2x80x94CF2xe2x80x94Oxe2x80x94CF2xe2x80x94CF2xe2x80x94SO3H.
The mobile acids of Formulae 1a, 1b, 1c, and 2 are made according to methods known in the art.
A third embodiment of the mobile acid component of the catalyst of this invention is adjunct acid mixtures (Bronsted/Lewis acid mixtures) such as HF/SbF5; HSO3F/SbF5; CF3SO3H/SbF5; HCF2CF2SO3H/SbF5; the SbF5 adjunct acid mixtures with the other mobile acids of Formulae 1a, 1b, 1c, and 2; and the corresponding compounds in which arsenic, niobium, or tantalum replaces the antimony. These compounds, known as xe2x80x9csuperacidsxe2x80x9d, are further described by Olah, et al., in Superacids, John Wiley and Sons, New York N.Y., see particularly pp. 7-11.
The stationary and mobile acid components are combined for use in the practice of this invention. In the practice of the present invention, the stationary acid is packed under anhydrous conditions into a column, equipped with temperature measurement and control systems, a means to supply a feed stock (such as a 90% butane/10% 1-butene mixture for an alkylation run) at a controlled rate, and a means to collect and analyze the effluent gas stream. Typically, analysis is by gas chromatography. The efficacy of the catalyst system, and the lifetime of the catalyst prior to deactivation, is measured in terms of the conversion of the olefin. In laboratory scale experiments, eluted mobile acid is conveniently trapped in a small bed of convenient base, such as sodium carbonate, prior to analysis. In larger scale experiments provision for trapping and recycling the mobile acid is provided. The eluted mobile acids are recovered and recycled by methods well known in the art, such as by aqueous extraction, removal of the water by distillation, and finally isolating the anhydrous mobile acid by distillation from concentrated sulfuric acid. The column is further provided with a means to inject accurately the mobile acid into the inlet end of the column. The amount of the mobile acid injected is conveniently described in terms of acid equivalents of mobile acid per acid equivalent of the stationary acid. The range is 100:1 to 0.01:1 equivalents mobile acid:equivalent stationary acid and preferably 10:1 to 0.1:1 equivalents mobile acid:equivalent stationary acid.
The present invention further comprises the use of the catalyst in alkylation, isomerization, and oligomerization processes. An example of an alkylation process is the economically very important reaction of isobutane and 1-butene to give isooctanes. An example of an oligomerization process is the conversion of propylene to C6 and C9 products. Catalysis of olefin oligomerization is described in detail by A. Corma in xe2x80x9cInorganic Solid Acids and Their Use in Acid-Catalyzed Hydrocarbon Reactions,xe2x80x9d in Chem. Rev 1995, 95, 559-614). Examples of isomerization processes are the conversion of 1-butene to 2-butene and of alpha-olefins to internal olefins. Catalysis of xcex1-olefin isomerization is described by M. A. Harmer, W. E. Farneth, and Q. Sun in xe2x80x9cTowards the Sulfuric Acid of Solids,xe2x80x9d in Advanced Materials, p. 1255-1257, 1998).
The terms xe2x80x9ccatalyst lifetimexe2x80x9d and xe2x80x9ctime to deactivationxe2x80x9d describe the time during which the catalyst acts effectively. For the purposes of this invention and the examples and comparative examples of this invention, catalyst lifetimes are compared using the time the catalyst is capable of producing an olefin conversion of 50% or greater. Such comparisons are made using the same feed composition, feed rate, column size and configuration, and column operating conditions.
The practice of this invention is now described by a specific example. A liquid phase mixture of 1-butene:i-butane (weight ratio 9:1) is passed through a vertical column containing a bed of the acid-containing modified silica or acid-entrapped silica, where 0.009 mL triflic acid per gram of the stationary acid bed has been applied to the inlet end of the column. This corresponds to 0.56 equivalents mobile acid/equivalent of stationary acid. The feed rate is 3 g of the 1-butene/i-butane mixture per gram of catalyst bed. The catalyst bed is operated at ambient temperature and 200 psig (1480 kPa). The product stream shows 100% conversion of the 1-butene to C5-C9 alkylation products, principally the C8 product, 2,2,4-trimethylpentane. Triflic acid eluted from the column is trapped in a sodium carbonate trap. The catalyst life is approximately 5 hours. The catalyst is reactivated by reapplying a fresh portion of triflic acid to the inlet end of the catalyst bed, thus demonstrating a simulation of a continuous process in which the mobile acid component is fed continuously into the stationary acid bed with the hydrocarbon fee at a rate sufficient to maintain the desired ratio of equivalents of mobile acid to equivalent of stationary acid. The eluted mobile acid is recovered, purified as necessary, and reintroduced to the column by methods known to those skilled in the art and, for example by aqueous extraction of the product stream, distillation to concentrate the mobile acid, and finally distillation from concentrated sulfuric acid to recover anhydrous mobile acid.
In a continuous modification of the process of this invention, triflic acid is fed with the alkane/alkene stream, at a rate sufficient to maintain catalytic activity, and recovered from the product stream by methods well known to those skilled in the art. For instance, Hommeltoft and Topsoe in EP 0 433 954 B1, for instance, describe a method for the recovery of triflic acid involving the steps of aqueous extraction, distillation, and finally distilling the triflic acid in the presence of concentrated sulfuric acid. Recovered triflic acid is then reinjected into the column in the liquid feed stream.
The catalyst of the present invention provides economies over prior art sulfuric acid processes and a marked reduction in process hazards over prior art hydrofluoric acid processes. Additionally, the catalyst of this invention provides a longer catalyst life over both the acid modified silica and the mobile acid supports of the prior art. By comparison with the mobile acid treated supports of the prior art, the amount of mobile acid required is substantially reduced.
The following materials are used in the Examples hereinafter:
1,1,2,2-tetrafluoroethanesulfonic acid is prepared from sodium hydrogen sulfate and tetrafluoroethane as described in U.S. Pat. No. 2,403,207.
NAFION, a perfluorinated ion exchange polymer, is available from E. I. du Pont de Nemours and Co., Wilmington Del. The preparation of a 13 wt % NAFION in silica (for Example 1) is given by Fraile, et al., in xe2x80x9cBis(oxazoline)-Copper Complexes, supported by Electrostatic Interactions, as Heterogeneous Catalysts for Enantioselective Cyclopropanation Reactions: Influence of the Anionic Support,xe2x80x9d in J. Catal., 186, 214-221 (1999). The NAFION silica catalyst is also commercially available as NAFION SAC 13 from E. I. du Pont de Nemours and Company in Wilmington Del.
Triflic acid, trifluoromethylsulfonic acid, is available from Aldrich Chemicals, Milwaukee Wis.
Silane-modified silica: The preparation of the acid-modified silica for Example 2 used Silica 60 and the procedure cited in Chem. Comm., 1997, 1803-1804, xe2x80x9cUnique silane modified perfluorosulfonic acids as versatile reagents for new solid acid catalysts.xe2x80x9d This procedure is also described by Harmer, et al., in U.S. Pat. No. 5,958,822.
Silica was obtained from Aldrich Chemicals, Milwaukee Wis. Silica 60, (Aldrich 28,863-2), 70-230 mesh (28-90 cm{circumflex over ( )}-1), about 500 m2/g surface area.
Sulfated zirconia was supplied by Magnesium Elektron, Inc. (MEI) as a commercial sample. The material was heated at 600xc2x0 C. for 2 hours before use.